The goal is to determine the ability of a number of strains of living and killed microorganisms and fractions derived from these microorganisms to inhibit tumor growth in the mouse. Bacterial strains have been selected which are known to alter tumor growth in both man and several animal models. Fractions will be selected which possess pharmacologic activities ranging from that of adjuvant to those more specific and direct. Both additive and synergistic combinations will be studied for an ability to cause regression where perhaps suppression is seen with individual components of a mixture. The tumors we shall study will be transplantable tumors derived from chemically induced murine sarcomas of high and low antigenicities as well as from a spontaneous murine malignant melanoma and a spontaneous murine mammary carcinoma. We shall determine whether the mechanism of action of the most promising combinations of treatment is immunological.